66861961 has 2 divisors, whose sum is σ = 66861962. Its totient is φ = 66861960.

The previous prime is 66861959. The next prime is 66861973. The reversal of 66861961 is 16916866.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 47334400 + 19527561 = 6880^2 + 4419^2 .

It is a cyclic number.

It is not a de Polignac number, because 66861961 - 2¹ = 66861959 is a prime.

Together with 66861959, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (66861911) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 33430980 + 33430981.

It is an arithmetic number, because the mean of its divisors is an integer number (33430981).

Almost surely, 2^66861961 is an apocalyptic number.

It is an amenable number.

66861961 is a deficient number, since it is larger than the sum of its proper divisors (1).

66861961 is an equidigital number, since it uses as much as digits as its factorization.

66861961 is an evil number, because the sum of its binary digits is even.

The product of its digits is 93312, while the sum is 43.

The square root of 66861961 is about 8176.9163503120. The cubic root of 66861961 is about 405.8756869035.

The spelling of 66861961 in words is "sixty-six million, eight hundred sixty-one thousand, nine hundred sixty-one".